1 // SPDX-License-Identifier: GPL-2.0-only
3 * Stack tracing support
5 * Copyright (C) 2012 ARM Ltd.
7 #include <linux/kernel.h>
8 #include <linux/export.h>
9 #include <linux/ftrace.h>
10 #include <linux/kprobes.h>
11 #include <linux/sched.h>
12 #include <linux/sched/debug.h>
13 #include <linux/sched/task_stack.h>
14 #include <linux/stacktrace.h>
17 #include <asm/pointer_auth.h>
18 #include <asm/stack_pointer.h>
19 #include <asm/stacktrace.h>
22 * AArch64 PCS assigns the frame pointer to x29.
24 * A simple function prologue looks like this:
29 * A simple function epilogue looks like this:
36 notrace void start_backtrace(struct stackframe *frame, unsigned long fp,
41 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
46 * Prime the first unwind.
48 * In unwind_frame() we'll check that the FP points to a valid stack,
49 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
50 * treated as a transition to whichever stack that happens to be. The
51 * prev_fp value won't be used, but we set it to 0 such that it is
52 * definitely not an accessible stack address.
54 bitmap_zero(frame->stacks_done, __NR_STACK_TYPES);
56 frame->prev_type = STACK_TYPE_UNKNOWN;
58 NOKPROBE_SYMBOL(start_backtrace);
61 * Unwind from one frame record (A) to the next frame record (B).
63 * We terminate early if the location of B indicates a malformed chain of frame
64 * records (e.g. a cycle), determined based on the location and fp value of A
65 * and the location (but not the fp value) of B.
67 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
69 unsigned long fp = frame->fp;
70 struct stack_info info;
75 /* Final frame; nothing to unwind */
76 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
82 if (!on_accessible_stack(tsk, fp, 16, &info))
85 if (test_bit(info.type, frame->stacks_done))
89 * As stacks grow downward, any valid record on the same stack must be
90 * at a strictly higher address than the prior record.
92 * Stacks can nest in several valid orders, e.g.
94 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
95 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
97 * ... but the nesting itself is strict. Once we transition from one
98 * stack to another, it's never valid to unwind back to that first
101 if (info.type == frame->prev_type) {
102 if (fp <= frame->prev_fp)
105 set_bit(frame->prev_type, frame->stacks_done);
109 * Record this frame record's values and location. The prev_fp and
110 * prev_type are only meaningful to the next unwind_frame() invocation.
112 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
113 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
115 frame->prev_type = info.type;
117 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
118 if (tsk->ret_stack &&
119 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
120 struct ftrace_ret_stack *ret_stack;
122 * This is a case where function graph tracer has
123 * modified a return address (LR) in a stack frame
124 * to hook a function return.
125 * So replace it to an original value.
127 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
128 if (WARN_ON_ONCE(!ret_stack))
130 frame->pc = ret_stack->ret;
132 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
134 frame->pc = ptrauth_strip_insn_pac(frame->pc);
138 NOKPROBE_SYMBOL(unwind_frame);
140 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
141 bool (*fn)(void *, unsigned long), void *data)
146 if (!fn(data, frame->pc))
148 ret = unwind_frame(tsk, frame);
153 NOKPROBE_SYMBOL(walk_stackframe);
155 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
157 printk("%s %pSb\n", loglvl, (void *)where);
160 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
163 struct stackframe frame;
166 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
177 if (!try_get_task_stack(tsk))
180 if (tsk == current) {
181 start_backtrace(&frame,
182 (unsigned long)__builtin_frame_address(0),
183 (unsigned long)dump_backtrace);
186 * task blocked in __switch_to
188 start_backtrace(&frame,
189 thread_saved_fp(tsk),
190 thread_saved_pc(tsk));
193 printk("%sCall trace:\n", loglvl);
195 /* skip until specified stack frame */
197 dump_backtrace_entry(frame.pc, loglvl);
198 } else if (frame.fp == regs->regs[29]) {
201 * Mostly, this is the case where this function is
202 * called in panic/abort. As exception handler's
203 * stack frame does not contain the corresponding pc
204 * at which an exception has taken place, use regs->pc
207 dump_backtrace_entry(regs->pc, loglvl);
209 } while (!unwind_frame(tsk, &frame));
214 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
216 dump_backtrace(NULL, tsk, loglvl);
220 #ifdef CONFIG_STACKTRACE
222 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
223 void *cookie, struct task_struct *task,
224 struct pt_regs *regs)
226 struct stackframe frame;
229 start_backtrace(&frame, regs->regs[29], regs->pc);
230 else if (task == current)
231 start_backtrace(&frame,
232 (unsigned long)__builtin_frame_address(1),
233 (unsigned long)__builtin_return_address(0));
235 start_backtrace(&frame, thread_saved_fp(task),
236 thread_saved_pc(task));
238 walk_stackframe(task, &frame, consume_entry, cookie);